I don't have an image, but here's the idea:

Standard Mecha'thun Mage

The Cards

Have at least two of these cards in your opening hand: Zola, 2x Galvanizer, 2x Youthful Brewmaster, 2x Ancient Brewmaster. The Coin counts as a setup card if you have 2 other setup cards as well in your opening hand.

Other cards you need: Hex Lord Malacrass, Mecha’thun and Pyroblast

There are substitutions and additions to make this deck more consistent(like Simulacrum and Baleful Banker), but this is a Bad HS Combo. We don't need consistency.

Malacrass

If you had 3 or more setup cards in your opening hand, play Malacrass once.

If you only had 2 setup cards in your opening hand, you need to wait until you have 10 mana and a Youthful Brewmaster in your hand, and then you play Malacrass, bounce it back to your hand with Youthful Brewmaster and play Malacrass again next turn.

The Plan

Once you have Mecha’thun in your hand: play Galvanizers and bounce them back to your hand with the other setup cards. You need to play a total of 10 Galvanizers, so the combo will in total require at least 4-6 setup turns, depending on your opening hand.

An Example - Worst Case Scenario(that still works):

I’ll assume you only had 2 Ancient Brewmasters in your opening hand, and you have no coin.

First Galvanizer turn: With 2 Galvanizers, Zola and 1 Ancient Brewmaster and Mecha’thun in hand, play: Galvanizer, Zola on Galvanizer, Ancient Brewmaster on Galvanizer.

First Malacrass turn: With Malacrass and 1 Youthful Brewmaster in hand, play Malacrass and bounce it back with Youthful Brewmaster. You can play your first malacrass turn earlier than this if you want.

Second Galvanizer turn: With 2 Ancient Brewmasters, 3 Galvanizers and Mecha’thun in hand, play: discounted Galvanizer, Ancient Brewmaster on Galvanizer, discounted Galvanizer, Ancient Brewmaster on Galvanizer.

Second Malacrass turn: Play Malacrass. You can play this turn earlier if you want.

Third Galvanizer turn: Same as second Galvanizer turn

Fourth Galvanizer turn: With 1 Ancient Brewmaster, 1 Youthful Brewmaster, 3 Galvanizers and Mecha’thun in hand, play: discounted Galvanizer, Ancient Brewmaster on Galvanizer, discounted Galvanizer, Youthful Brewmaster on Galvanizer, Galvanizer, Galvanizer, Galvanizer.

Combo Turn: With no cards in your deck, no minions on your board, and only a 0-cost Mecha’thun and a Pyroblast in hand: Play Mecha’thun and kill it with Pyroblast.

Rank 1 Legend EZ, and it’s only a 10 card combo over 7 turns :)

EDIT: To see a 7 card combo with 1 setup turn, check out my comment. There's finally a use for Snap Freeze!